A claw pump includes a pair of rotors which have hook-shaped claws formed thereon and rotate in opposite directions to each other at the same speed in a non-contact manner while maintaining an extremely narrow clearance therebetween inside a housing that forms a pump chamber. The two rotors form a compression pocket, and compressed gas compressed in the compression pocket is discharged through a discharge port. The claw pump continuously performs suction, compression, and exhaust without using a lubricating oil or sealing liquid, thereby producing a vacuum state or pressurized air. As described above, since the lubricating oil or the like is not used, there are advantages that clean gas can be exhausted and discharged, and a higher compression ratio than that of a Roots pump that does not have a compression stroke can be realized.
FIG. 5 illustrates an example of a claw pump according to the related art. In FIG. 5, a claw pump 100 includes a housing 102 that forms a pump chamber therein, and the housing 102 has a cross-sectional shape of two partially overlapping circles. Both end faces of the housing 102 are blocked by side plates (not illustrated), and a suction port 108 is formed in a circumferential wall of the housing 102. Two parallel rotating shafts 110a and 110b are provided inside the housing 102, and rotors 112a and 112b are respectively fixed to the rotating shafts 110a and 110b. The rotors 112a and 112b are provided with hook-shaped claws 114a and 114b which mesh each other in a non-contact manner.
The rotors 112a and 112b rotate in opposite directions to each other (arrow directions), and gas g is suctioned into an inlet pocket P0 that communicates with the suction port 108. Thereafter, a first pocket P1 and a second pocket P2 are formed as the rotors 112a and 112b rotate (see FIG. 5(D)). Furthermore, the first pocket P1 and the second pocket P2 join and form a compression pocket P (see FIG. 5(F)).
The compression pocket P is reduced as the rotors 112a and 112b rotate. A discharge port 116 is formed in one of the side plates at a position that communicates with the reduced compression pocket P. The gas g is compressed in the compression pocket P and is discharged from the discharge port 116.
In a case where the claw pump is used as a vacuum pump, during an operation at a suction pressure of atmospheric pressure, the pressures of the inlet pocket P0, the first pocket P1, and the second pocket P2 are maintained substantially at the atmospheric pressure. During a compression stroke after the compression pocket P is formed, the compression pocket P reaches the atmospheric pressure or higher. When the pressure of the rotor on the downstream side in the rotational direction is higher than the pressure on the upstream side, counter torque is generated in the rotor in a direction opposite to the rotational direction of the rotor.
During an operation at a suction pressure of the ultimate pressure, the pressures of the inlet pocket P0, the first pocket P1, and the second pocket P2 are maintained at the ultimate pressure (for example, about 7000 Pa [absolute pressure] although the ultimate pressure varies depending on the pump type). The pressure of the compression pocket P is maintained at the ultimate pressure until the discharge port 116 is open to the atmospheric pressure. However, when the discharge port 116 starts to be opened, air flows back to the compression pocket P and reaches the atmospheric pressure. Therefore, the pressure of the rotors 112a and 112b on the downstream side becomes higher than that on the upstream side, and the counter torque increases.
Patent Literature 1 discloses an example of a claw pump. A housing of the claw pump is constituted by a cylinder having a cross-sectional shape of two partially overlapping circles, and two side plates which block both ends of the cylinder. Discharge ports are provided at positions that are open to the compression pocket and are formed in both the side plates forming a pair in order to improve discharge efficiency.